1. Field of the Invention
The present invention relates to metal powder, a method for producing the same and conductive paste. More particularly, the invention relates to conductive paste, for example, which is advantageously used for forming internal conductors of monolithic ceramic electronic components, a metal powder contained therein and a method for producing such metal powder.
2. Description of the Related Art
A conductive paste is used for forming internal conductors of monolithic ceramic electronic components, such as monolithic ceramic capacitors. The conductive paste contains metal powder as a conducting component. As the metal powder, nickel powder is frequently used.
As the size and thickness of such monolithic ceramic electronic components is decreased, the particle size of the metal powder contained in the internal conductor must be decreased.
One method for advantageously producing a metal powder having a small particle size is a vapor phase process. However, the production cost of metal powder is high in the vapor phase process.
On the other hand, a method for producing metal powder having a small particle size by a liquid phase process is disclosed, for example, in Japanese Examined Patent Publication No. 6-99143. The patent publication discloses a method for producing nickel powder in which a powder having a small particle size is obtained by the step of subjecting a nickel salt solution to liquid-phase reduction using a solution of a boron hydroxide such as sodium boron hydroxide as a reducing agent. In accordance with this method, however, since boron precipitates as an alloy or impurity in the nickel powder, the resultant nickel powder is not always suitable as a conductive component for conductive paste.
A method for producing metal powder by a liquid phase process is also disclosed in Japanese Unexamined Patent Publication No. 5-43921. The patent publication discloses a method for producing nickel powder in which a solution containing basic nickel carbonate is reduced and hydrazine is used as a reducing agent. Since hydrazine is used as a reducing agent, nickel powder will not be contaminated with impurities. However, the resultant nickel powder has a particle size of more than 100 nm and thus being undesirable as a conductive component for a conductive paste for forming internal conductors in which the thickness thereof must be decreased.